A semiconductor package (produced by a so-called build-up system) has been known in the prior art and is shown in FIG. 3. In the built-up system a film-like circuit pattern 22 is overlaid via a film-like insulation layer (resist) 18 on a core member 10 carrying a circuit pattern 12 made of metallic foil on the surface thereof, and electrically connected to the circuit pattern 12 on the core member 10 to form a multilayer circuit. The circuit pattern 12 provided on the surface of the core member 10 is made, for example, of copper foil. A solder resist 26 is coated on the upper surface of the uppermost film-like circuit pattern 22. A ball bump 30 is fixed to the circuit pattern 22 at a position where the solder resist 26 is partially removed. Thus, the semiconductor package is formed. A semiconductor chip 14 is fixed to the film-like circuit pattern 22 in the uppermost layer and connected to the multilayer circuit. Further, the semiconductor chip 14 or others are sealed by a potting substance (not shown) to form a semiconductor device.
According to the above semiconductor package, since the multilayer circuit is formed by using the film-like resist 18 and the film-like circuit pattern 22, it is possible to make the package very dense and miniaturize the circuits in response to the dense integration of the semiconductor chip 14.
However, when the semiconductor package is produced by the build-up system as described above, the bonding force between the coated resist 18 and the copper-plated film-like circuit pattern 22 is weak. That is, since the film-like circuit pattern 22 is merely overlaid with the resist 18, the bonding force is very weak and is, for example, in a range from 0.2 kg/cm to 0.3 kg/cm.
Accordingly, a bonding force is also weak between the ball bump 30 fixed on the surface of the film-like circuit pattern 22 and the resist 18. Since the semiconductor chip 14 is fixed to the uppermost film-like circuit pattern 22 via the ball bump 30, the semiconductor chip 14 cannot be assuredly fixed, with a high yield, to the semiconductor package and this results in a problem of lack of reliability and durability. For example, when the ball bump 30 is fixed, the film-like circuit pattern 22 may be peeled off or the semiconductor chip 14 may be released from the semiconductor package to disconnect the electric connection between the semiconductor chip 14 and the multilayer circuit.
Also, when the semiconductor chip is connected to the multilayer circuit of the semiconductor package by a wire bonding system, there is problem in that, if the bonding ability of the film-like circuit pattern 22 with the resist 18 is inferior, it is impossible to bond wires to the film-like circuit pattern 22 with a high yield to result in the deterioration of reliability and durability.